1. Technical Field
Embodiments of the present disclosure relate to micro-electromechanical (MEMS) devices, and in particular, MEMS devices having suspended membranes.
2. Description of the Related Art
Membrane MEMS devices, such as pressure sensors and microphones, are used in various applications. Typically, membrane MEMS devices, such as the device 10 shown in FIG. 1, includes a structural layer 12 having a portion that is supported by a substrate 14 and a portion forming a suspended membrane 13 that is separated from the substrate 14 by a cavity 16.
In some cases, membrane MEMS devices are fabricated using surface micromachining to release or suspend the membrane. Generally described, surface micromachining includes forming a sacrificial layer on a surface of a substrate. A structural layer is then formed on the sacrificial layer. Openings are formed in the structural layer, and the sacrificial layer is removed through the openings thereby releasing the membrane and forming a cavity.
For various applications, the cavity is sealed from atmosphere and set at a particular pressure. In that regard, the openings used to remove the sacrificial layer will be closed, sealing the cavity.
In the past, the openings have been closed by an indirect sealing, such as is shown in the device 10 of FIG. 1. In particular, a cover 18 is provided over the structural layer 12 so that the space within the cover 18, including the cavity 16, is sealed from atmosphere. The cover 18 may be secured to the substrate 14, such as by anodic bonding.